Hip fractures, wherein the femur is fractured one or more times in the area of the femur or immediately adjacent the head are comparatively common. A great many devices have been proposed for the reduction of fractures of this type. While many of these devices have found the application and have advantages relative one to another, there remain some problems and areas of continuing concern.
Such reduction devices consist, basically, of an elongate lag screw which is threaded on one end to be threadably received in the head of the femur, and is secured to a plate such that when the lag screw is tightened, the head of the femur is forcibly compressed at the fracture line to the remainder of the femur.
It has also been recognized that various adjustment features are important in treating certain femoral fractures. In general, fastener devices with such adjustment features employ a guide sleeve which is imbedded in one bone segment, such as the upper segment of the femur, in order to receive and adjustably hold one end of an axially elongated shaft, e.g. a lag screw, which extends through both fractured bone segments, with the end of the shaft opposite the guide sleeve being provided with structure for securing the shaft to the head of the femur. Because of absorption occurring during the healing process, it has been necessary, in some instances, to accommodate a certain amount of telescoping movement between the shaft and the guide sleeve.
Functionally, some of these devices perform quite satisfactorily for many fractures of the femur but are extremely difficult for the surgeon to properly implant. It is, therefore, of great importance to provide a fixation device which is not only functional in providing the necessary stability and guidance in the reduction of the fracture, but can be efficiently, accurately and quickly implanted by the surgeon.
A compression hip screw assembly is used to apply compression across a proximal femoral fracture. The assembly includes a lag screw, a barrel, a plate and cortical screws to attach the plate to bone. A compression hip screw may be used to allow for sliding compression of the lag screw so that the fracture could be adequately reduced under normal weight bearing. The applying of force to the fracture site promotes healing. This phenomenon is known as Wolff's law. By providing a load to the fracture site atrophy of the fracture site can be avoided.
When load is applied to a compression hip screw, the screw which has a tendency to back out laterally through the plate or to cut out medially through the head of the femur.
When the screw threads tend to advance medially, such phenomenon is known as cutout. The screw tends to advance medially and may cause problems to the compression of the fracture site and may move medially to the point of having the screw leave the bone or femur.
Alternatively the screw threads of the hip screw during compression may back out or move away from the head of the femur in a lateral direction.
Such movement of the threads of the lag screw may cause the lag screw to move against the plate and eventually to have a portion of the lag screw extend past the plate and cause soft tissue irritation and other difficulties to the patient.
A compression hip screw is used to allow for sliding compression of the lag screw so that the fracture can be adequately reduced under normal weight bearing. In prior art lag screws the lag screws may often compress too far and laterally back out of the barrel creating soft tissue irritation and femoral head collapse. In some indications, the surgeon may prefer the lag screw be fixed with respect to the barrel so that it is not able to provide sliding compression. For example, in a sub-trochanteric fracture or reverse oblique fracture, the surgeon would prefer the lag screw and barrel to be rigid. The surgeon must choose between having a compression hip screw or a fixed hip screw in the surgery room, or the surgeon may require that both be present.
To assist in preventing cutout, while providing compression, the screw may be permitted to slide along the barrel but not rotate in the barrel. Such configurations have been provided that provide for anti-rotation features positioned between the barrel and the screw. Some devices require different lag screws or barrels to be inserted depending on the surgeon's requirements to limit compression, rotation, or both. For example, a separate lag screw or barrel may be required to prevent rotation by requiring the keying of the barrel to the screw.
Other attempts to provide for keying or preventing rotation between the screw and the barrel include the use of clips, locking pins, ribs or tabs. These configurations require the use of complex insertion and removable tools, odd cross-sectional designs, and may increase the amount of lag screw and barrel inventory required by the medical facility.